The field of the disclosure relates generally to power conversion systems and, more particularly, to direct current (DC)-to-DC power converters and power converter configurations for renewable energy facilities.
At least some of known electric power generation facilities are configured to use renewable energy sources for generation of electric power. Examples of such facilities include most solar power generation facilities, most geothermal power generation facilities, and some wind power generation facilities. Most known renewable energy generation facilities, for example, solar power generation facilities include photovoltaic (PV) arrays that generate low voltage direct current (LVDC) power, e.g., in a range between approximately 0.6 kilovolts (kV) and approximately 1.5 kV. Such known solar facilities also include a power conversion system, i.e., a LVDC solar collector system that converts the collected DC power to alternating current (AC). Such known LVDC solar collector systems include a plurality of strings, where each string includes a PV array and a DC-to-AC (DC/AC) power converter coupled to the PV array. The DC/AC power converters are configured to convert the LVDC power to AC power at a low voltage value of approximately 600 volts AC (VAC). Each string also includes a step-up transformer configured to increase the 600 VAC power to a medium voltage (MV) within a range between approximately 2 kV and approximately 34.5 kV and a downstream circuit breaker between the transformer and a MV bus. The MV power is further stepped-up to a higher AC voltage suitable for use on an AC electric power grid system, e.g., a high voltage (HV) of approximately 345 kV. Since each solar power generation facility may include a large number of such strings, construction and maintenance costs for such facilities are substantially increased.
Such known LVDC solar collector systems have a relatively narrow band of flexibility with respect to regulating the voltage and power outputs of the solar arrays prior to transformation to AC and the subsequent voltage step-ups. Specifically, there is substantially no voltage and power control mechanisms between the solar arrays and the DC/AC power converters, where the circuit breakers in the strings provide for coarse power control. Also, the switching devices of the DC/AC power converters typically have low frequency switching rates, thereby inhibiting integration of maximum power point tracking (MPPT) features into the control strategy of the individual strings of the LVDC solar collector systems. Moreover, the primary fault protection feature for each string is the associated string circuit breaker which may be configured to isolate the associated string after a predetermined period of time, and the protective features may be unidirectional.